It has been known to administer plural medical liquids through a tubular set that is generally in the form of a Y. U.S. Pat. Nos. 3,886,937 and 4,034,754 describe duckbill check valves in one arm of the Y set upstream of the crotch of the Y, sometimes called a side port, for a secondary liquid source. As shown in U.S. Pat. No. 4,034,754, the secondary liquid container on the right is placed slightly higher than the primary liquid container on the left. Very slight pressure changes in the Y set caused by changing liquid levels opens and closes the check valve to sequentially administer the tube liquids.
While the concept is known to use a backflow check valve in such administration set, there have been problems in leakage and sensitivity. The duckbill type valves as described in U.S. Pat. No. 3,886,937 and 4,034,754 have experienced problems in sticking closed or not completely shutting off; i.e., liquid will still bleed to the primary container when the check valve should be closed.
A preloaded disk valve which is distortably urged against a valve seat is also described in U.S. Pat. No. 3,886,937. However, such preloaded valve has sluggish response in that a relatively large differential head pressure is needed in the primary container to open such valve. Also, it is difficult in manufacturing to accurately control the precise preloading necessary so the valve is not overloaded or underloaded.
A specially molded valve member with depending feet structure is described in U.S. Pat. No. 4,005,710. This valve requires an expensive molding process to get its unique shape. In addition, its large cylindrical side surface, which includes an outer surface of the legs, sometimes tends to cling to the vertical housing wall causing the valve member to stick in either the open or closed position. It must be recognized that the pressure differential between the two liquid containers might be as small as 2 inches of water and this is not sufficient to refloat the valve member stuck to the side wall of the housing by liquid surface tension.
Other background prior art includes U.S. Pat. Nos. 2,999,499 and 2,538,552, which again includes massive molded movable valve members of a special T-shape. Such valves, as shown in U.S. Pat. No. 2,999,499, may be adequate for response to extremely high pressure injections from a piston type syringe, but again would be sluggish in response to minute changes in head pressure between two gravity feed containers.
In addition to the problem caused by very low pressure differentials in medical liquid administration sets, the flow rates vary over a wide range up to 500 ml/hr. or more. It has previously been thought necessary to provide wide throated valves with large passages to handle this high flow rate in an administration set.